In recent years, with the rapid development in the information industry, various data processing systems have been developed. Recording methods and apparatus suitable for these data processing systems have accordingly been developed and employed. Among these recording methods, the heat transfer recording system employes a light-weight, compact and noiseless apparatus which can be easily operated with little maintainance. In this system, color data can also be dealt with. In recent years, this recording system has been widely used. The heat transfer recording system can be roughly divided into two types, i.e., the heat melt type and the heat mobile type. In the latter type of heat transfer recording system, heat is applied in a predetermined pattern to a lamination of a heat transfer dye-providing material comprising (a) a support having thereon a dye-providing layer containing a binder and a heat-mobile dye with (b) a heat image-receiving material, from the dye-providing material support side. The heat-mobile dye is thereby transferred to the recording medium (heat transfer image-receiving material) in the predetermined pattern to obtain a transfer image.
The term "heat-mobile dye" as used herein means a dye capable of being transferred from a heat transfer dye-providing material to a heat transfer image-receiving material by sublimation or diffusion in the medium.
The heat transfer image-receiving material for use in this heat mobile type of heat transfer recording system normally comprises an organic solvent-soluble polymer. However, the use of organic solvents is not desirable because it causes an increase in the manufacturing cost and harms the health of workers. Therefore, the use of water-dispersed polymers has been attempted. However, these water-dispersed polymers cannot provide a sufficient reception of dyes. Therefore, in order to obtain a high density transfer image, an excessive amount of heat is required for transfer, causing deterioration in the durability of a thermal head.
In order to obtain a high transfer density, the incorporation of a polymer such as polyvinylpyrrolidone and hydroxyethyl cellulose in a saturated polyester have been proposed as disclosed in JP-A-57-107885 and JP-A-57-137191 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, this approach does not take into consideration the preservability of the resulting transfer image under irradiation with light (light resistance). In other words, when the transfer image is stored under a room fluorescent light over an extended period of time or exposed to sunshine, it often suffers from a drastic drop in image density or a remarkable discoloration. It has heretofore been known that an ultraviolet light absorbent may be incorporated in an image-receiving material to improve the light resistance thereof as disclosed in JP-A-59-158289, JP-A-60-101090, and JP-A-61-229594. When an ultraviolet light absorbent is singly incorporated in an image-receiving material, it is dispersed entirely in an image-receiving layer. Since a transferred dye is present mainly on the surface of the image-receiving layer, the ultraviolet light absorbent thus incorporated cannot sufficiently attain its effect. When a large amount of such an ultraviolet light absorbent is incorporated in the image-receiving material to improve the light resistance thereof, it causes the dye developed to be easily dispersed, causing a bleeding in the image or heat fusion to an ink sheet.
An image-receiving material comprising a water-dispersed polymer is also disadvantageous in that it often causes heat fusion to the heat transfer dye-providing material during transfer. In order to overcome these disadvantages, various approaches have been proposed. For example, the incorporation of a polymer such as polyvinylpyrrolidone and hydroxyethyl cellulose in a saturated polyester is proposed in JP-A-57-107885 and JP-A-57-137191. Furthermore, JP-A-58-148794, JP-A-58-197089, and JP-A-58-188695 propose the incorporation of finely divided silica grains, synthetic sodium aluminosilicate, light calcium carbonate, etc. in an image-receiving material.
In these approaches, however, it is difficult to provide an image-receiving material which can provide a high-density transfer image and exhibit an excellent film quality inhibiting heat fusion to a heat transfer dye-providing material.